Display for 3D images

Abstract: An autostereoscopic display comprises first and second displays (1a, 1b, 300a, 300b) and an observer tracking system (34) for tracking the position of an observer. A beam combiner (4) combines light from the first and second displays. Each of the displays comprises a light source (300a, 300b) and a spatial light modulator (1a, 1b) for modulating light from its light source (300a, 300b) with left or right two dimensional images. Each of the light sources (300a, 300b) comprises, in sequence, an extended source of illumination (303), a shutter (302) and an imaging system (301). The imaging systems (301) image light from the sources of illumination (303) via the shutters (302) at a first viewing region. The imaging systems (301) are fixed and the shutters (302) are moveable so that the first viewing region tracks the position of an observer.

Description: The present invention relates to a display for three dimensional images. Known display devices for producing three dimensional (3D) images create the illusion of a 3D opaque object by displaying a number of two dimensional (2D) images to the observer. Each of the 2D images is a view of the object from a particular direction and, during reproduction of the 3D image, each component 2D image is replayed in its respective direction. The freedom of movement of the viewer location is limited by the total angular range over which the views are imaged. Known displays capable of imaging only a low number of 2D views provide a 3D image within a highly restricted range of viewing angles. Consequently the viewer is constrained to be within a limited range of positions in order to maintain the appearance of a 3D image. Similarly, the number of observers of a 3D image may also be restricted due to the limited number of 2D views. "Subjective Assessments of the Resolution of Viewing Directions in a Multi Viewpoint 3D TV System", S. Pastoor, K. Schenke, p 217 Proc. SID Vol. 30/3 1989 describes the requirement for the number of views in a 3D display. It is estimated that, for a typical scene, 60 or more views may be required in an interocular spacing. For a wide field of view, several hundred views will have to be displayed at some time. It is currently not possible to achieve this with a simultaneous view presentation type of display. A display described by Akiyama.K, and Tetsutani.N in a paper titled "Three dimensional visual communication" 1991 ITE Annual convention, p607, has a two view display produced by providing an interlaced image on a liquid crystal device (LCD) behind a lenticular screen. The position of an observer is monitored and, as the observer moves from an orthoscopic viewing zone to a pseudoscopic viewing zone, the sequence in which the images are interlaced is reversed so as to maintain the appearance of an orthoscopic image to the observer. Such a system requires precise tracking of the observer's head so as to determine the time at which the image sequence should be reversed. Further, such a display is limited to use by a single observer and the black mask of the LCD is made visible by the lenticular screen. EP-A-0 404 289 "Television set or the like for creating a three dimensional perception of images and apparatus for creation of same" describes a 3D display in which a lenticular screen is moved with respect to a high resolution display device in response to movement of an observer. Such an apparatus requires very precise control of the motion of the lenticular screen and is limited for use by a single observer. GB 2 206 763 discloses a 3D display apparatus of the temporally multiplexed type in which 2D images representing views taken from different directions are supplied to an LCD. A spatially modulated light source such as a cathode ray tube (CRT) is disposed in the focal plane of a lens disposed adjacent the LCD. Different regions of the CRT screen are illuminated in synchronism with the different 2D images displayed by the LCD so that the views are visible in the directions from which they were taken. US Patent No. 4 649 425 discloses, in Figures 7 and 8, a display device according to the preamble of claim 1. Cathode ray tubes are used as the first and second displays. US Patent No. 2 883 906 discloses a display device. The display device of US Patent No. 2 883 906 does not have an observer tracking system. According to a first aspect of the invention, there is provided an autostereoscopic display apparatus as defined in the appended Claim 1. Preferred embodiments of the invention are defined in the other appended claims. It is thus possible to provide an autostereoscopic display for displaying a 3D image which can track the movement of one or more observers. The or each observer has a substantially increased degree of freedom of movement within which the 3D image is visible. The present invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram illustrating the general principles of a display apparatus using a beam combiner; Figure 2 is a schematic diagram showing the apparatus of Figure 1 in use with two observers; Figure 3 is a schematic diagram illustrating the general principles of a projection display apparatus; Figure 4 is a schematic diagram of a display apparatus incorporating an observer tracking system; Figure 5 is a schematic diagram of another comparative display apparatus; Figure 6 is a schematic diagram of a display apparatus constituting an embodiment of the invention; Figure 7 shows part of the display of Figure 6 in more detail; and Figure 8 shows a modification of the display of Figure 6. Figure 1 shows a plan view of a comparative example of a direct view 3D display incorporating a beam combiner. First and second image data are presented to first and second spatial light modulators 1a and 1b, respectively, for production of first and second 2D images. Each of the first and second spatial light modulators 1a and 1b is illuminated by a respective movable illuminator 2a and 2b providing movable sources of illumination. Light from the illuminators 2a and 2b is directed by respective lenses 3a and 3b towards the spatial light modulators 1a and 1b. The light is intensity modulated by the spatial light modulators 1 a and 1b to form two 2D images. In order to create a 3D image, the 2D images are of the same object or objects, but from different directions. The images are then combined by a beam combiner 4 to create the 3D image. The sources of illumination 2a and 2b are arranged to produce light emanating from the positions indicated at "A" with the observer at position 1 as shown in Figure 1. If, however, the observer moves to position 2, then the light emanates from the positions "B" in order to maintain the appearance of a 3D image. Thus the relative positions of the sources of illumination 2a and 2b with respect to the lenses 3a and 3b adjacent the SLMs 1a and 1b are controlled in response to movement of the observer. The display may be controlled so as to maintain the appearance of a 3D image in response to movement by the observer, but maintaining the same point of view. Alternatively, the image data presented to the SLMs may be modified in response to movement of the observer so as to present appropriate new views, for example to simulate movement around an object. The display of Figure 1 is also suitable for use with a plurality of observers, as shown in Figure 2. The illuminators 2a and 2b comprise a plurality of light sources arranged such that two or more light sources can be in use simultaneously. Both viewers can then view the same 3D image simultaneously and from the same point of view. In an example, each of the spatial light modulators may be a 250mm diagonal dimension liquid crystal device (LCD). The illuminators may be spaced 500mm from the respective LCDs and the optical path length from the LCDs to the observer position may be nominally one metre. The illuminators may then consist of illuminator elements 32.5mm wide (so that the window size at the observer is nominally 65mm wide) which perform translatory movement, or which are switched on and off so as to simulate movement in a step wise manner, in response to lateral movement of the observer, at half the speed of the observer. The optical system, i.e. the lenses 3, SLMs 1 and the beam combiner 4, make efficient use of the light available from the illuminators 2a and 2b, giving rise to a bright image. Figure 3 shows the general principles of a projection display apparatus. Apparatuses of this type are disclosed in an earlier British Patent Application No. 9323402.9. As described hereinabove, image data for two views are presented to two SLMs 1a and 1b. The SLMs spatially modulate light from respective illuminators to form two 2D images which are then combined by a beam combiner 4. However, instead of being directly viewed by the observer, the illuminators are imaged into the aperture of a projection lens 10. The total output numerical aperture defines the maximum angular extent of the output view directions when the final image screen is a lens. However, if a combination of first and second lenticular screens 12 and 14 acting as an angular amplifying element is used as an output element, as shown, then output lobes are generated by the second lenticular screen 14 enhancing the total viewing cone of the display. The first lenticular screen 12 is arranged to form an image at a diffuser 16. The diffuser 16 lies in the object plane of the second lenticular screen 14. As with the other embodiments described hereinbefore, the positions of the illuminators are controlled so as to track the movement of the at least one observer. In an example display system, 50mm LCD screens are imaged by an 80mm f#1.9 projection lens to a 250mm image size at a 3:1 angular amplifying screen. The observer distance from the screen will be 1000mm with approximately 200mm lateral freedom of movement. Vertical movement can be accommodated in a number of ways. The illuminator image at the viewer plane can be vertically extended, thereby giving a wide range of possible viewing heights from which the image can be seen. The at least one illuminator may provide vertically extended sources of illumination or a vertical diffuser element may be provided at the output screen plane. Alternatively, the position of the at least one source of illumination may be moved vertically in correspondence with the movement of the observer or observers. Tilting of the observer's head can be accommodated, in displays which do not use arrays of (cylindrical) lenticules, by tilting the or each source of illumination. However, the image has to be modified in order to maintain the 3D autostereoscopic effect. Similarly, the size of the illuminated area of the or each illuminator may be altered if the or each illuminator is moved longitudinally in response to longitudinal movement of the observer, so as to compensate for the change in the angle subtended at the observer's eyes. Various types of tracking systems may be used so as to control the tracking of one or more observers by the display. For instance, the or each observer may communicate his position by way of an input device such as a joy stick. In another embodiment, the or each observer's position may be sensed by an ultrasonic tracking system or the or each observer may wear a magnet to indicate his position to a magnetic tracking system. In a further embodiment, one or more cameras may scan the viewing region to determine the or each observer's position, for instance supplying image data to a system which recognises the eyes of the or each observer. In yet a further embodiment, the or each observer wears a reflector which reflects electromagnetic energy, such as infrared energy. A scanning infrared source and an infrared detector or a wide angle infrared source and a scanning infrared detector determine the position of the or each reflector which is preferably worn between the eyes of the observer. In a still further embodiment, the or each observer may issue voice commands, such as UP,LEFT,HERE etc to direct the display or to allow an audio controlled tracking system to identify the position of the source of the observer's voice. Figure 4 shows the principles of operation of a display system incorporating an observer tracking system. Image data, representing multiple views of an object 26 captured by a plurality of cameras 28 or generated by computer 30, are presented via an image controller to a system controller 32. The system controller 32 is responsive to the position of an observer as determined by an observer tracking detector 34. The system controller 32 issues instructions to an illuminator position controller 36 to control the illuminators. The system controller 32 also determines which of the views are reproduced by the spatial light modulators of the autostereoscopic 3D display 38. Figure 5 shows a further example of a comparative projection display apparatus. Image data for two views are presented to spatial light modulators 40a and 40b. Each of the spatial light modulators is illuminated by a respective movable illuminator 42a and 42b. Light from the illuminator 42a is directed onto the spatial light modulator 40a via a lens 44a. Similarly light from the illuminator 42b is directed onto the spatial light modulator 40b via a lens 44b. The images formed at the spatial light modulators 40a and 40b are imaged onto an angular amplifying element 46 (for example of the type comprising first and second lenticular screens 12 and 14 and a diffuser, as described hereinabove with reference to Figure 3). The images are imaged through respective lenses 48a and 48b whose apertures are superimposed at a beam combiner 50. Such superimposition of the images substantially eliminates keystone distortion of the two images relative to each other. This arrangement enables two spatial light modulators to be imaged in a beam combiner configuration without the need for a projection lens having a large back working distance. Figure 6 shows an embodiment of the invention. This is an autostereoscopic 3D display of a type similar to that shown in Figure 1 and comprising SLMs 1a and 1b and a beam combiner 4. However, the illuminators 2a and 2b and the lenses 3a and 3b are replaced by compact light sources 300a and 300b, each of which comprises a lens array 301 such as a lenticular screen behind which is disposed an array of slits forming a shutter 302 and an extended source of illumination 303 (Figure 7). The lenticular screen 301 may alternatively be replaced by a parallax barrier. Each lenticule of the lenticular screen is aligned with a respective slit so as to control the direction of illumination of the spatial light modulator 1a or 1b so that the left and right images are viewable by the left and right eyes, respectively, of an observer 305 located at a viewing region of the display. The shutter 302 is connected to a mechanical actuator 304. A tracking system for tracking the position of the observer 305 supplies control signals to the actuator 304 so as to position the shutter 302 with respect to the lens array 301 so that the observer 305 can see the 3D image. The illumination source 303 and the shutter 302 thus form a movable source of illumination and the lens array 301 forms an imaging system for imaging the source of illumination at the observer 305. Figure 8 illustrates an alternative arrangement for tracking an observer in which the mechanically movable shutter 302 and the actuator 304 are replaced by a programmable shutter 306. The programmable shutter 306 may, for instance, comprise a LCD SLM which is controlled so as to provide transparent slits whose positions are movable in response to movement of the observer 305 so that the 3D image tracks the observer. Compact light sources of the type shown in Figures 6 to 8 may be used in place of the corresponding components in the other arrangements shown in Figures 3 and 5 the drawings so as to provide relatively compact displays which are capable of tracking one or more than one observer.

Claims: An autostereoscopic display for displaying a three dimensional image, comprising an observer tracking system (34) for tracking the position of an observer, first and second displays (1a, 1b, 300a, 300b) for displaying left and right two dimensional images, respectively, a beam combiner (4) for combining light from the first and second displays (1a, 1b, 300a, 300b), first and second shutters (302) and first and second imaging systems (301) for imaging light at a first viewing region, the first and second shutters (302) being movable with respect to the first and second imaging systems (301), respectively, so that the first viewing region tracks the position of the observer determined by the observer tracking system; characterised in that the first and second displays (1a, 1b, 300a, 300b) comprise first and second extended sources of illumination (303) and first and second spatial light modulators (1a, 1b) for modulating light from the first and second extended sources of illumination (303) with the left and right two dimensional images, respectively, the first and second extended sources of illumination (303) being arranged in sequence with the first and second shutters (302) and the first and second imaging systems (301), the first and second imaging systems (301) being lens arrays or parallax barriers for imaging light from the first and second sources of illumination (303) via the first and second shutters (302), respectively, at the first viewing region, the first and second imaging systems (301) being fixed and the first and second shutters (302) being movable so that the first viewing region tracks the position of the observer determined by the observer tracking system. A display as claimed in claim 1, characterised in that each of the first and second imaging systems (301) comprises a lens array. A display as claimed in claim 2, characterised in that each of the lens arrays (301) comprises a lenticular screen. A display as claimed in claim 1, characterised in that each of the first and second imaging systems (301) comprises a parallax barrier. A display as claimed in any one of the preceding claims, characterised in that each of the first and second shutters (302) comprises an array of slits. A display as claimed in any one of the preceding claims, characterised by a mechanical actuator (304) responsive to the observer tracking system (34) for moving the first and second shutters (302) with respect to the first and second imaging systems (301), respectively.

Inventors: EZRA DAVID, WOODGATE GRAHAM JOHN, EZRA, DAVID, WOODGATE, GRAHAM, JOHN
Applicants: SHARP KK
Application year: 1994
Main classification: G02B27
IPC codes: H04N13, G02B27